1. Field of the Invention
The present invention generally relates to a booklet stacker to stack multiple booklets, a ring-binding device including the booklet stacker, a ring-binding system including an image forming apparatus and the ring-binding device, and a booklet stacking method.
2. Discussion of the Background Art
At present, finishers to perform post-processing, such as aligning, sorting, stapling, punching, and/or bookbinding, of multiple sheets of recording media discharged from image forming apparatuses, such as copiers, printers, facsimile machines, or multifunction devices including at least two of these functions, are widely used.
In the field of bookbinding, ring binding is widely used. Ring binding involves punching an end portion of a bundle of sheets and then binding the bundle of sheets together using a binder including metal or plastic rings or coils. At present, a need has arisen for various types of bookbinding of sheets of recording media discharged from image forming apparatuses. Accordingly, there is a need for finishers or post-processing apparatuses to perform various types of post-processing.
In response to such a need, ring-binding devices that can perform ring binding online (i.e., automatically) have come to be used in addition to conventional bookbinding devices that perform end-stitching, that is, stapling one edge portion of sheets. There are ring-binding devices that include a booklet stacker to stack multiple bundles of sheets each of which is bound with a ring member (hereinafter “ring-bound booklets”). In such ring-binding devices, a greater number of booklets can be stacked, which obviates the need to remove the finished booklets from the ring-binding device frequently, thus increasing efficiency in ring binding.
However, conventional booklet stackers like that shown in FIG. 11 suffer from a flaw. The is, conventional booklet stackers typically simply pile ring-bound booklets 100 one on another on a booklet stacker 34X as shown in FIG. 11, and as a result ring members 28X binding the respective booklets 100 overlap or interfere with each other. Consequently, it is difficult to increase the number of booklets stacked on the booklet stacker 34X because the pile of multiple booklets tilts. Additionally, when multiple booklets 100 are stacked on the booklet stacker 34X, any given ring member 28X can damage adjacent booklets 100 piled on and under that ring member 28X. As the pile of multiple booklets 100 tilts, the booklets 100 should be aligned again after the booklets 100 are removed from the booklet stacker 34X. If not aligned again, handling of the booklets 100 becomes difficult because the tilted pile of booklets 100 cannot be packed neatly or transported safely.
In view of the foregoing, for example, in JP-2008-280170-A, a ring-binding device including a mechanism to move the stack tray vertically (e.g., an elevation mechanism) has been proposed. More specifically, this ring-binding device includes a discharge member to discharge booklets through a discharge port to the stack tray, the elevation mechanism to move the stack tray vertically, an upper-end sensor to detect an upper end of the booklets stacked on the stack tray, and a controller to control the elevation mechanism according to results of detection by the upper-end detector. The controller controls the elevation mechanism so that the upper end of the booklets stacked on the stack tray is aligned with a reference position disposed at a predetermined vertical distance from the discharge port. Thus, the stack tray is moved to a position at a given vertical distance from the discharge port so that the booklet can be discharged through the discharge port onto the stack tray smoothly.
However, although generally successful at conveying the booklet smoothly from the discharge port to the stack tray, this approach does not address the problem of overlap or interference of the ring members 28X binding the respective booklets described above. Consequently, the pile of booklets cannot be kept flat, and thus the number of booklets that can be stacked on the stack tray is limited. Further, this approach does not address the damage to the booklets caused by the ring members or the need to realign the booklets after removal from the stack tray.
In view of the foregoing, the inventors of the present invention recognize that there is a need to keep the piled ring-bound booklets flat on the stack tray, to prevent damage to the booklets, and to facilitate good alignment of the booklets after removal from the stack tray.